Optical modulator

Abstract

An optical modulator is provided with a ridge-shaped optical waveguide formed of a dielectric thin film having electro-optic effect, a buffer layer covering the optical waveguide, a signal electrode formed on the buffer layer so as to be opposed to the optical waveguide through the buffer layer; a ground electrode formed on the buffer layer together with the signal electrode, and a dielectric film having a higher dielectric constant than air and covering at least a part of exposed surfaces of the signal electrode and ground electrode and exposed surfaces of the buffer layer.

What is claimed is: 
     
       1. An optical modulator comprising:
 a ridge-shaped optical waveguide formed of a dielectric thin film having electro-optic effect; 
 a buffer layer covering the optical waveguide; 
 a signal electrode formed on the buffer layer so as to be opposed to the optical waveguide through the buffer layer; 
 a ground electrode formed on the buffer layer together with the signal electrode; and 
 a dielectric film having a dielectric constant higher than air and covering at least a part of exposed surfaces of the signal electrode and ground electrode and exposed surfaces of the buffer layer, wherein 
 at least a part of the dielectric film in an inter-electrode area between the signal electrode and the ground electrode is removed together with the buffer layer. 
 
     
     
       2. The optical modulator as claimed in  claim 1 , wherein the dielectric constant of the dielectric film is higher than the dielectric constant of the buffer layer. 
     
     
       3. An optical modulator comprising:
 a ridge-shaped optical waveguide formed of a dielectric thin film having electro-optic effect; 
 a buffer layer covering the optical waveguide; 
 a signal electrode formed on the buffer layer so as to be opposed to the optical waveguide through the buffer layer; 
 a ground electrode formed on the buffer layer together with the signal electrode; and 
 a dielectric film having a dielectric constant higher than air and covering at least a part of exposed surfaces of the signal electrode and ground electrode and exposed surfaces of the buffer layer, wherein 
 the dielectric film is formed on an upper surface of the buffer layer, and the signal electrode and the ground electrode are formed on an upper surface of the dielectric film. 
 
     
     
       4. The optical modulator as claimed in  claim 3 , wherein the dielectric constant of the dielectric film is higher than the dielectric constant of the buffer layer. 
     
     
       5. An optical modulator comprising:
 a ridge-shaped optical waveguide formed of a dielectric thin film having electro-optic effect; 
 a buffer layer covering the optical waveguide; 
 a signal electrode formed on the buffer layer so as to be opposed to the optical waveguide through the buffer layer; 
 a ground electrode formed on the buffer layer together with the signal electrode; and 
 a dielectric film having a dielectric constant higher than air and covering at least a part of exposed surfaces of the signal electrode and ground electrode and exposed surfaces of the buffer layer, wherein 
 the optical waveguide includes first and second waveguides constituting a Mach-Zehnder interferometer, 
 the signal electrode includes a first signal electrode opposed to the first waveguide through the buffer layer and a second signal electrode opposed to the second waveguide through the buffer layer, 
 the ground electrode includes a first ground electrode provided in the vicinity of the first signal electrode on a side opposite to the second signal electrode with respect to the first signal electrode and a second ground electrode provided in the vicinity of the second signal electrode on a side opposite to the first signal electrode with respect to the second signal electrode, 
 upper and both side surfaces of each of the first and second signal electrodes and upper and side surfaces of each of the first and second ground electrodes are not covered with the dielectric film, and 
 an upper surface of the buffer layer in a first inter-electrode area between the first and second signal electrodes is covered with the dielectric film. 
 
     
     
       6. The optical modulator as claimed in  claim 5 , wherein the upper surface of the buffer layer in a second inter-electrode area between the first signal electrode and the first ground electrode and a third inter-electrode area between the second signal electrode and the second ground electrode is covered with the dielectric film. 
     
     
       7. The optical modulator as claimed in  claim 5 , wherein the dielectric constant of the dielectric film is higher than the dielectric constant of the buffer layer. 
     
     
       8. The optical modulator as claimed in  claim 5 , wherein
 an upper surface of the buffer layer in a second inter-electrode area between the first signal electrode and the first ground electrode and a third inter-electrode area between the second signal electrode and the second ground electrode is not covered with the dielectric film. 
 
     
     
       9. An optical modulator comprising:
 a ridge-shaped optical waveguide formed of a dielectric thin film having electro-optic effect; 
 a buffer layer covering the optical waveguide; 
 a signal electrode formed on the buffer layer so as to be opposed to the optical waveguide through the buffer layer; 
 a ground electrode formed on the buffer layer together with the signal electrode; and 
 a dielectric film having a dielectric constant higher than air and covering at least a part of exposed surfaces of the signal electrode and ground electrode and exposed surfaces of the buffer layer, wherein 
 the optical waveguide includes first and second waveguides constituting a Mach-Zehnder interferometer, 
 the signal electrode includes a first signal electrode opposed to the first waveguide through the buffer layer and a second signal electrode opposed to the second waveguide through the buffer layer, 
 the ground electrode includes a first ground electrode provided in the vicinity of the first signal electrode on a side opposite to the second signal electrode with respect to the first signal electrode and a second ground electrode provided in the vicinity of the second signal electrode on a side opposite to the first signal electrode with respect to the second signal electrode, 
 an upper surface of the buffer layer in a first inter-electrode area between the first and second signal electrodes is not covered with the dielectric film, and 
 upper and outer side surfaces of each of the first and second signal electrodes, upper and side surfaces of each of the first and second ground electrodes and an upper surface of the buffer layer in a second inter-electrode area between the first signal electrode and the first ground electrode and a third inter-electrode area between the second signal electrode and the second ground electrode are covered with the dielectric film. 
 
     
     
       10. The optical modulator as claimed in  claim 9 , wherein
 inner side surfaces of each of the first and second signal electrodes are not covered with the dielectric film. 
 
     
     
       11. The optical modulator as claimed in  claim 9 , wherein inner side surfaces of each of the first and second signal electrodes are covered with the dielectric film. 
     
     
       12. The optical modulator as claimed in  claim 9 , wherein the dielectric constant of the dielectric film is higher than the dielectric constant of the buffer layer. 
     
     
       13. An optical modulator comprising:
 a ridge-shaped optical waveguide formed of a dielectric thin film having electro-optic effect; 
 a buffer layer covering the optical waveguide; 
 a signal electrode formed on the buffer layer so as to be opposed to the optical waveguide through the buffer layer; 
 a ground electrode formed on the buffer layer together with the signal electrode; and 
 a dielectric film having a dielectric constant higher than air and covering at least a part of exposed surfaces of the signal electrode and ground electrode and exposed surfaces of the buffer layer, wherein 
 the optical waveguide includes first and second waveguides constituting a Mach-Zehnder interferometer, 
 the signal electrode includes a first signal electrode opposed to the first waveguide through the buffer layer and a second signal electrode opposed to the second waveguide through the buffer layer, 
 the ground electrode includes a first ground electrode provided in the vicinity of the first signal electrode on a side opposite to the second signal electrode with respect to the first signal electrode and a second ground electrode provided in the vicinity of the second signal electrode on a side opposite to the first signal electrode with respect to the second signal electrode, 
 an upper surface of each of the first and second signal electrodes, an upper surface of each of the first and second ground electrodes, and an upper surface of the buffer layer in a second inter-electrode area between the first signal electrode and the first ground electrode and a third inter-electrode area between the second signal electrode and the second ground electrode are not covered with the dielectric film, and 
 both side surfaces of each of the first and second signal electrodes, the side surface of each of the first and second ground electrodes and an upper surface of the buffer layer in a first inter-electrode area between the first and second signal electrodes are covered with the dielectric film. 
 
     
     
       14. The optical modulator as claimed in  claim 13 , wherein the dielectric constant of the dielectric film is higher than the dielectric constant of the buffer layer.